1. Technical Field
The present invention generally relates to ultrasound imaging systems, and more particularly to an ultrasound imaging system and a method of forming a plurality of scan lines and frames by using receiving signals provided by transducers in a probe.
2. Background Art
The ultrasound imaging system shows internal structures of a target object in a non-invasive and non-destructive manner. The ultrasound imaging system includes a probe to transmit and receive ultrasound signals and a beam former. In the probe, transducers are equipped to perform the mutual conversion of ultrasound signals and electric signals. When equipping a plurality of transducers, an outspread of the ultrasound can be prevented more effectively compared to a case of equipping a single transducer. Further, with the plurality of the transducers, the ultrasound signals can be focused and the sensitivity may be improved. The transducers may generate the ultrasound signals one by one. Alternatively, some transducers may generate the ultrasound signals at a time. The ultrasound signals transmitted from the transducers are reflected at a discontinuous surface of acoustic impedance, i.e., at a surface of a reflector in a target. Each transducer converts echo ultrasound signals into the electric signals.
The ultrasound signals must be focused when transmitting and receiving. When transmitting, the transmission order of the transducers may be determined by considering the distance differences between the transducers and the focal point. Thus, the ultrasound signals transmitted from all of the transducers, which contribute to form one scan line, reach the focal point at the same time with the same phase. Accordingly, the focused ultrasound signals (i.e., the summation of ultrasound signals at the focal point) may have the maximum amplitude. The ultrasound echoes reflected from the focal point reach each transducer at different times. Thus, when receiving, time delays are applied to the ultrasound echoes so that the echo ultrasound signals can be seen as those arriving simultaneously at the transducers with the same phase.
A large number of focal points are required to improve the image resolution. However, this causes the degradation of the frame rate since the same procedures should be repeatedly performed as much as the number of focal points for forming an image. A receive dynamic focusing is introduced to solve the problem described above. According to the receive dynamic focusing, the number of focal points are fixed in transmission focusing, whereas the number of focal points are varied in receiving focusing in order to focus more finely. However, the improvement in resolution is also limited due to the fixed number of focal points when transmitting. In U.S. Pat. No. 6,231,511, all the signals obtained by performing transmission focusing on a number of adjacent scan lines are used in the receiving focus. This is to obtain the same effect as the case where focal points exist in all the points on the scan line.
Referring to FIG. 1, a conventional ultrasound system generally includes a probe 110, a transmitting unit 120, a receiving unit 130, an intra-channel processing unit 140, a receiving focusing unit 150, an image processing unit 160, a displaying unit 170 and a controlling unit 180. The probe 110 includes a plurality of transducers. The receiving unit 130 and the intra-channel processing unit 140 are equipped and provided as much as the number of transducers.
The transmitting unit 120 generates pulse voltages, which have different time delays, in consideration of the relative positions of the transducers. Each transducer 111 in the probe 110 receives the pulse voltage from the transmitting unit 120 and generates transmitting ultrasound signals. The transmitting ultrasound signals from the transducers are focused on focal points on the transmission scan lines. Referring to FIG. 2, the ultrasound signals generated from the transducers-4 to 4 in section A are focused on a focal point f0 at a scan line L0, while the ultrasound signals generated from the transducers-2 to 6 in section B are focused on a focal point f2 at a scan line L2.
Each transducer receives the ultrasound echoes originated from the ultrasound signals transmitted along the scan lines. For instance, some ultrasound signals transmitted from the transducer 0 along the scan line L0 arrive at a first point P1 when a time corresponding to a path Z1 passes. Then, the ultrasound signals are received at the transducer 0 as the ultrasound echoes when the time corresponding to the path Z1 passes again. Some ultrasound signals transmitted from the transducer 2 along the scan line L2 arrive at the first object point P1 when a time corresponding to a path Z2 passes. Then, the ultrasound signals are received at the transducer 0 as the ultrasound echoes when the time corresponding to the path Z1 passes. That is, the transducer 0 receives the ultrasound echoes, which are originated from the ultrasound signals transmitted along scan lines L0 and L2, respectively.
Referring back to FIG. 1, transducers 111 convert the ultrasound echoes into the electric receiving analog signals. The receiving unit 130 amplifies the electric receiving analog signals and converts the amplified electric receiving analog signals into digital signals. The intra-channel processing unit 140 stores the digital signals of the respective scan lines, delays the digital signals and focuses the delayed digital signals.
Referring to FIG. 3, the intra-channel processing unit 140 includes buffer memories 141 equipped and provided as much as the number of scan lines, a delaying & interpolating units 142 corresponding to the buffer memories one by one and an apodizing unit 143. Each buffer memory 141 stores the digital signal inputted from the receiving unit 130. For example, the digital signals, which are obtained from the ultrasound echoes received at transducer 0, are separated according to the transmitting scan lines L0 and L2. Thus, the separated digital signals are stored in different buffer memories. The delaying & interpolating unit 142 delays the digital signals by considering the arriving time of ultrasound echoes at each transducer. An apodizing unit 143 includes an intra channel apodization value calculating unit 143a to provide appropriate weight values to the digital signals of each scan line, multiplying units 143b to apply the weight values to the digital signals and an adding unit 143c to sum the outputs from multiplying units 143c. 
As shown in FIG. 1, the receiving focusing unit 150 includes an intra-channel apodization value calculating unit 151 to provide appropriate weight values to outputs of the intra channel processing unit 140, i.e., to the digital signals of each transducers, multiplying units 152 to apply the weight values to the digital signals and an adding unit 153 to sum the outputs from multiplying units 152 and to output the focused data of all the transducers 111.
The image processing unit 160 processes the focused data outputted from the receiving focusing unit 150 in various manners. The displaying unit 170 displays ultrasound images with the processed data. The controlling unit 180 controls the operations of transmitting unit 120 and the image processing unit 160.
Each buffer memory 141 of the intra channel processing unit 140 in the conventional ultrasound system described above should have the storage capacity suitable for storing the digital signals per scan line. Generally, the storage capacity should be at least 60 Kbit. Further, the buffer memories 141 are required as much as the scan lines, conventionally over 128. Thus, each intra channel processing unit 140 should have a memory, the storage capacity of which surpasses 7 Mbit.